Ethanol-sensitive adenosine receptor-dependent cAMP production occurs in nerve cells and lymphocytes. This system is stimulated acutely by ethanol, and inhibited by chronic exposure to ethanol. In this study, cAMP production is measured in freshly isolated lymphocytes as a biologic marker of alcoholism and in cultured lymphocytes as a possible phenotypic marker for patients who might be at risk to develop alcoholism. Alcoholics who are dependent on alcohol appear to have a depressed response to adenosine receptor activation.